The present invention relates to egg yolk-containing, oil-in-water emulsified foods such as mayonnaise, tartar sauce and dressings, having reduced cholesterol contents.
A demand for reduced-cholesterol foods has been increasing in recent years. However, oil-in-water emulsified foods such as mayonnaise, tartar sauce and dressings, whose main ingredient is egg yolk, inevitably contain at least a certain level of cholesterol. This is because egg yolk itself contains approximately 1.2% of cholesterol and also because some vegetable oils, which may be added as another essential ingredient, contain low levels of cholesterol.
Heretofore, there have been proposed mayonnaise-like foods which are produced without using egg yolk to attain the reduction of cholesterol level (Japanese Patent Laid-Open Publication No. 39341/1995, etc.). In the production of foods of this type, one cannot make use of the excellent emulsifying effect egg yolk has, and thus one should instead add emulsifiers or emulsion stabilizers such as starch, when required. Besides, these foods are lacking in the characteristic flavor and rich taste (superior taste) of egg yolk. Thus, yolk-free, mayonnaise-like foods that are satisfactory from the viewpoint of taste have not been obtained to date.
Further, there have also been proposed oil-in-water emulsified foods which are produced by using substantially the same level of egg yolk as in conventional mayonnaise but which have reduced cholesterol contents. For instance, a method for producing an oil-in-water emulsified food from reduced-cholesterol egg yolk is proposed in Japanese Patent Laid-Open Publication No. 23918/1996. According to this method, egg yolk and an edible oil are firstly mixed; from the resultant mixture, the edible oil is then removed by separation to obtain reduced-cholesterol egg yolk wherein approximately 40 to 90% of the cholesterol originally contained in the egg yolk has been extracted; and the reduced-cholesterol egg yolk is used in an amount of approximately 5 to 25% to produce an oil-in-water emulsified food. The oil-in-water emulsified food thus obtained however still contains at least 6xc3x9710xe2x88x923% of cholesterol.
Furthermore, Japanese Patent Laid-Open Publication No. 137209/1999 describes a method for producing an oil-in-water emulsified food, characterized in that low-cholesterol egg yolk obtained by subjecting egg yolk to processing with supercritical carbon dioxide to reduce its cholesterol content by approximately 60 to 95% is used together with enzymatically processed egg yolk. In this method, however, enzymatically processed egg yolk, from which cholesterol has not been removed, is used in an amount of 0.5% or more, so that the resulting oil-in-water emulsified food still contains more than 6xc3x9710xe2x88x923% of cholesterol.
Thus, there have not yet been succeeded in producing, using conventional levels of egg yolk, oil-in-water emulsified foods having reduced cholesterol contents of less than 6xc3x9710xe2x88x923%.
Under these circumstances, we made studies to overcome the aforementioned drawbacks in the prior art, and came up with the idea of using, as an egg yolk ingredient of an oil-in-water emulsified food, low-cholesterol dried egg yolk according to Japanese Patent No. 3081038, obtainable by subjecting egg yolk to enzymatic processing, followed by processing with supercritical carbon dioxide. We continued our studies and found the following: if egg yolk is directly subjected to processing with supercritical carbon dioxide, almost all cholesterol contained in the egg yolk can be removed, but the egg yolk loses its emulsifying effect to a significant extent. This is probably because proteins and the like contained in egg yolk are severely damaged and modified in the course of the processing with supercritical carbon dioxide. However, we considered that if egg yolk is subjected to enzymatic processing for improving its emulsifying effect prior to the processing with supercritical carbon dioxide, it must be possible for us to prevent, to some extent, the egg yolk from losing its emulsifying effect in the course of the processing with supercritical carbon dioxide, whereby processed egg yolk containing almost no cholesterol can successfully be obtained while retaining the emulsifying effect. We further carried out our studies and came to have such a thought that if the processed egg yolk obtained in the above-described manner is used, an oil-in-water emulsified food containing almost no cholesterol can be obtained even if the egg yolk level is nearly equal to that in conventional mayonnaise.
To confirm this thought, we tried variously to prepare oil-in-water emulsified foods with the use of the egg yolk substantially free from cholesterol, obtained by subjecting egg yolk first to enzymatic processing and then to processing with supercritical carbon dioxide. The emulsified foods thus obtained were found to have poor emulsion stability, that is, they were readily separated into aqueous phase and oil phase during storage.
Meanwhile, Japanese Patent Laid-Open Publication No. 199559/1989 discloses a related technique. This technique, relating to a method for producing low-cholesterol dressings, is characterized in that egg yolk which has been subjected to processing for reducing cholesterol and also to phospholipase processing is used together with gelatinized starch. Admittedly, this publication describes the use of xe2x80x9cmodified egg yolk containing substantially no cholesterol.xe2x80x9d However, with respect to the reduction of emulsion stability caused by the use of the egg yolk which has been subjected to processing for reducing cholesterol, the publication fails to describe any means for solving this problem, or even to mention this problem. The reason for this is probably as follows: as the dressings described in this publication have an egg yolk content lower than that of conventional mayonnaise, and contain gelatinized starch which is considered to be effective in improving emulsion stability, the inventors of the prior art did not notice at all that egg yolk loses its emulsifying effect to a significant extent when subjected to processing for reducing cholesterol.
Objects of the present invention are therefore to provide an oil-in-water emulsified food having a dramatically reduced cholesterol content but having a high egg yolk content, having emulsion stability high enough to prevent separation into aqueous phase and oil phase during storage, and having the characteristic flavor and rich taste (superior taste) of egg yolk, and to provide a method for producing such oil-in-water emulsified foods.
We made extensive studies in order to attain the above objects, and, as a result, have found that an oil-in-water emulsified food having high emulsion stability and scarcely undergoing separation during storage can be obtained if processing with supercritical carbon dioxide, to which the egg yolk already enzymatically processed is subjected, is so controlled that the resulting processed egg yolk can have a cholesterol content not lower than a specific level. The present invention has been accomplished on the basis of this finding.
The present invention, in a first aspect, therefore provides an oil-in-water emulsified food having an egg yolk content as calculated in terms of raw egg yolk of 2.8% or more, a content of cholesterol derived from egg yolk of 7xc3x9710xe2x88x924% or more, and a total cholesterol content of less than 6xc3x9710xe2x88x923%.
The present invention, in a second aspect, provides a method for producing an oil-in-water emulsified food, comprising the steps of subjecting an egg yolk fluid to enzymatic processing, thereby converting phospholipids contained in the egg yolk into lysophospholipids; subjecting the enzymatically processed egg yolk to processing for reducing cholesterol, thereby obtaining processed dry egg yolk still retaining at least 0.1% of cholesterol; and mixing the processed dry egg yolk with other ingredients in an amount of at least 0.7% of all the ingredients used, thereby obtaining the above-described oil-in-water emulsified food.
We followed up our studies and have newly found the following fact: the oil-in-water emulsified food obtained by the above-described method is stable and can remain unchanged over a long period of time when stored at low temperatures around 10xc2x0 C.; however, when stored at approximately 20xc2x0 C., although it remains unchanged over 3 to 4 months, it tends to undergo separation due to partial destruction of its emulsified state when stored for 5 months or more. We therefore made studies furthermore in order to solve this problem and have found that the oil-in-water emulsified food which further contains egg white in an amount of 6% or more as calculated in terms of raw egg white is stable and remains unchanged even when stored at normal temperature for a prolonged period of time (at 20xc2x0 C. for 5 months or more). Alternatively, the oil-in-water emulsified food further containing 0.03% or more of xanthane gum has also been found stable over a longer period of time.
Therefore, the present invention, in another aspect, provides an oil-in-water emulsified food having an egg yolk content as calculated in terms of raw egg yolk of 2.8% or more, an egg white content as calculated in terms of raw egg white of 6% or more, a content of cholesterol derived from egg yolk of 7xc3x9710xe2x88x924% or more, and a total cholesterol content of less than 6xc3x9710xe2x88x923%.
The present invention, in a further aspect, provides an oil-in-water emulsified food having an egg yolk content as calculated in terms of raw egg yolk of 2.8% or more, a xanthane gum content of 0.03% or more, a content of cholesterol derived from egg yolk of 7xc3x9710xe2x88x924% or more, and a total cholesterol content of less than 6xc3x9710xe2x88x923%.
The present invention, in a still further aspect, provides a method for producing an oil-in-water emulsified food, comprising the steps of subjecting an egg yolk fluid to enzymatic processing, thereby converting phospholipids contained in the egg yolk into lysophospholipids; subjecting the enzymatically processed egg yolk to processing for reducing cholesterol, thereby obtaining processed dry egg yolk still retaining at least 0.1% of cholesterol; and mixing the processed dry egg yolk with egg white or xanthane gum and other ingredients in amounts of at least 0.7%, and at least 6% as calculated in terms of raw egg white or at least 0.03%, respectively, based on all the ingredients used, thereby obtaining the above-described oil-in-water emulsified food.
In this specification, xe2x80x9c%xe2x80x9d means xe2x80x9c% by weightxe2x80x9d, unless otherwise specified.
The oil-in-water emulsified food according to the present invention is composed of aqueous phase ingredients and oil phase ingredients present in the form of an emulsion of oil-in-water type. In other words, the emulsified food of the invention is such an emulsion that oil droplets are dispersed in an aqueous phase, and specifically includes mayonnaise, tartar sauce and emulsion-type dressings. In the present invention, 10-90% of aqueous phase ingredients and 90-10% of oil phase ingredients are mixed, these percentages varying depending upon the objective food. In general, 20-70% of aqueous phase ingredients and 80-30% of oil phase ingredients are mixed.
The egg yolk content as calculated in terms of raw egg yolk of the oil-in-water emulsified food according to the present invention is 2.8% or more. The term xe2x80x9cegg yolkxe2x80x9d as used herein refers not only to raw or dried egg yolk but also to processed liquid or dry egg yolk obtained by subjecting raw or dried egg yolk to enzymatic processing, processing for reducing cholesterol, or the like. If the egg yolk content as calculated in terms of raw egg yolk is less than 2.8%, the oil-in-water emulsified food, final product, becomes poor in emulsion stability, so that it tends to undergo separation during storage, and, in addition, the product hardly has the characteristic flavor and rich taste of egg yolk. When the egg yolk content is 4.8% or more, the flavor and taste of the product become comparable to those of conventional mayonnaise; this egg yolk content range is therefore more preferred. However, if the egg yolk content is in excess of 30%, the product has a taste greatly different from that of conventional mayonnaise.
The oil-in-water emulsified food of the present invention has a content of cholesterol derived from egg yolk of 7xc3x9710xe2x88x924% or more, and a content of cholesterol derived from all the ingredients including egg yolk (referred to as xe2x80x9ctotal cholesterol contentxe2x80x9d in the present invention) of less than 6xc3x9710xe2x88x923%. Those oil-in-water emulsified foods having an egg yolk-derived cholesterol content of less than 7xc3x9710xe2x88x924% are poor in emulsion stability, and readily undergo separation during storage. Further, those oil-in-water emulsified foods having a total cholesterol content of 6xc3x9710xe2x88x923% or more cannot be a solution of the problems in the prior art as mentioned previously in connection with Japanese Patent Laid-Open Publication No. 23918/1996 and the like.
In the present invention, cholesterol contents were measured in accordance with xe2x80x9cCholesterol Quantitative Analytical Method Axe2x80x9d described in xe2x80x9cAnalysis Manualxe2x80x9d included in xe2x80x9cStandard Tables of Food Composition in Japanxe2x80x9d published in January, 1997 by the Food Composition Section of Resources Council, Science and Technology Agency, Japan.
In one aspect of the present invention, the oil-in-water emulsified food contains egg white in an amount of 6% or more as calculated in terms of raw egg white. The term xe2x80x9cegg whitexe2x80x9d as herein used refers to an egg fluid obtained by separating egg yolk from a whole egg; specifically, it refers to raw egg white, sterilized egg white, egg white obtained by thawing frozen egg white, egg white obtained by reconstituting dried egg white with water, or the like. If the egg white content as calculated in terms of raw egg white of the oil-in-water emulsified food, final product, is less than 6%, the product tends to undergo separation due to partial destruction of its emulsified state that may occur during storage at normal temperature for a prolonged period of time (at 20xc2x0 C. for 5 months or more); such a product is not acceptable as an emulsified product. When the egg white content as calculated in terms of raw egg white is 7% or more, the oil-in-water emulsified food has separation resistance comparable to that of conventional mayonnaise; this egg white content range is therefore more preferred. However, if the egg white content is in excess of 20%, the product has a taste greatly different from that of conventional mayonnaise.
In another aspect of the present invention, the oil-in-water emulsified food contains at least 0.03% of xanthane gum instead of egg white. If the oil-in-water emulsified food, final product, contains less than 0.03% of xanthane gum, the product tends to undergo separation due to partial destruction of its emulsified state that may occur during storage at normal temperature for a prolonged period of time (at 20xc2x0 C. for 5 months or more); such a product is not suitable as an emulsified product. When the xanthane gum content is 0.05% or more, the oil-in-water emulsified food can have separation resistance comparable to that of conventional mayonnaise, so that this xanthane gum content range is more preferred. However, the separation resistance effect peaks at the xanthane gum content of 0.3%, so that the addition of more than 0.3% of xanthane gum is not practical.
If both egg white and xanthane gum are used together in amounts within the above-described ranges, the resulting oil-in-water emulsified food of the invention shows higher resistance to separation.
Into the oil-in-water emulsified food of the present invention, phytosterols which have the action of lowering blood cholesterol levels may be incorporated. Examples of phytosterols useful herein include xcex1-sitosterol, xcex2-sitosterol, stigmasterol, ergosterol and campesterol, and derivatives thereof such as fatty esters thereof, ferulic esters thereof and glycosides thereof.
It is said that the intake of phytosterols required to lower blood cholesterol levels is generally at least 0.4 g per day and that Japanese individuals take approximately 15 g of mayonnaise at one meal. This means that if phytosterols are incorporated into the oil-in-water emulsified food (mayonnaise) of the present invention so that 15 g of the mayonnaise contains at least 0.4 g of phytosterols (i.e., the content of phytosterols in the mayonnaise is 2.7% or more), it becomes possible to lower blood cholesterol levels by taking the mayonnaise only once a day. However, if the phytosterols content exceeds 10%, the oil-in-water emulsified food tends to become rough and unpleasant to the tongue.
A method for producing such an oil-in-water emulsified food of the present invention will be described hereinafter.
Raw egg yolk, or an egg yolk fluid prepared, for example, by reconstituting dried egg yolk with water is firstly subjected to enzymatic processing to convert phospholipids contained in the egg yolk into lysophospholipids. An enzyme usually used for the enzymatic processing is phospholipase A. If egg yolk is processed using phospholipase A, this enzyme acts on the constitutive phospholipids of egg yolk lipoproteins (complexes composed of egg yolk lipids such as egg yolk phospholipids and egg yolk proteins; main component of egg yolk), and the fatty acid residue in position 1 or 2 of the phospholipids is hydrolyzed; the phospholipids are thus converted into lysophospholipids. For example, the enzymatic processing can be carried out at a pH between 6 and 8, at a temperature between 45xc2x0 C. and 55xc2x0 C. for about 2 to 12 hours with the enzyme concentration adjusted to approximately 1xc3x9710xe2x88x924 to 2xc3x9710xe2x88x922%.
In the present invention, the mass percentage of lysophosphatidylcholine on the total mass of lysophosphatidylcholine and phosphatidylcholine (hereinafter referred to as xe2x80x9clyso-percentagexe2x80x9d) determined by the IATROSCAN method (the TLC-FID method) after conducting the above-described enzymatic processing is preferably 10% or more, more preferably 30% or more. When enzymatically processed egg yolk whose lyso-percentage is less than 10% is used, the resulting oil-in-water emulsified food is readily cracked or undergoes separation, and, moreover, tends to become musty during long-term storage. On the other hand, if enzymatically processed egg yolk whose lyso-percentage is more than 90% is used, the resulting oil-in-water emulsified food tends to be somewhat bitter.
Subsequently, the enzymatically processed egg yolk fluid is subjected to processing for reducing cholesterol, using supercritical carbon dioxide. It is preferable to dry the enzymatically processed egg yolk fluid before subjecting it to the processing for reducing cholesterol. By doing so, it becomes possible to more efficiently conduct the processing for reducing cholesterol, using supercritical carbon dioxide. Any means can be employed to dry the enzymatically processed egg yolk, and it is enough to reduce the water content of the enzymatically processed egg yolk to approximately 1 to 6% by such a means as spray or freeze drying. In this step of drying, cholesterol contained in the egg yolk is also concentrated, and the resulting dried egg yolk is to have a cholesterol content of approximately 2 to 3%.
Supercritical carbon dioxide which is used for the above-described processing for reducing cholesterol refers to carbon dioxide at a temperature of 31.0xc2x0 C. (critical temperature) or more and at a pressure of 7.14 MPa (critical pressure) or more. Particularly preferred herein is supercritical carbon dioxide at a temperature between 35xc2x0 C. and 45xc2x0 C. and at a pressure between 13 MPa and 35 MPa.
The processing for reducing cholesterol, using such supercritical carbon dioxide may be conducted in a conventional manner. It is however necessary to control this processing so that the resulting processed dry egg yolk still retains a cholesterol content of 0.1% or more, more preferably 0.15% or more. If the processed dry egg yolk whose cholesterol content has been reduced to less than 0.1% is used, the resulting oil-in-water emulsified food is unstable and tends to undergo separation during storage although the reason for this is unknown.
A process for producing an oil-in-water emulsified food from the processed dry egg yolk that has been subjected to the processing for reducing cholesterol, and egg white and/or xanthane gum separately prepared is, if the objective food is mayonnaise, not different from the conventional mayonnaise production process. That is to say, after thoroughly mixing by stirring the processed dry egg yolk obtained in the above-described manner, egg white and/or xanthane gum, water, vinegar and other seasonings, edible oil is added to the mixture, and stirring is continued for emulsification. It is herein necessary that the processed dry egg yolk be incorporated in an amount of at least 0.7% of all the ingredients used. This is because the processed dry egg yolk in a small amount of less than 0.7% cannot impart the characteristic flavor and rich taste of egg yolk to the resulting oil-in-water emulsified food. It is noted that at least 0.7% of the processed dry egg yolk is equivalent to at least approximately 2.8% of raw egg yolk.
In the case where egg white is used, the egg white content of the oil-in-water emulsified food is 6% or more as calculated in terms of raw egg white, based on all the ingredients used. In the case where xanthane gum is used, the xanthane gum content of the oil-in-water emulsified food is 0.03% or more, based on all the ingredients used. By incorporating egg white and/or xanthane gum, it is possible to obtain an oil-in-water emulsified food that does not readily undergo separation even when stored at 20xc2x0 C. for 5 months or more.
In addition to the aforementioned ingredients, a variety of ingredients usually used for producing conventional emulsified foods may be used as ingredients of the oil-in-water emulsified food of the invention according to the type of the objective food. For example, if the emulsified food is mayonnaise, there may be used seasonings such as table salt and sugar, synthetic seasonings such as sodium glutamate, spices such as mustard powder and oil mustard, and the like. In the case where the emulsified food is tartar sauce, such ingredients as chopped pickles and onion may be added. Further, if a low-calorie mayonnaise-like food containing a reduced level of edible oil is an objective food, soybean proteins, starch, dextrin, cellulose, etc. can be incorporated.